1. Field of the Invention
The present invention relates to a cover for an airbag device including a tear line splitting when an airbag is inflated.
2. Description of the Related Art
Airbag devices are known that are installed in predetermined positions such as instrument panels and steering wheels of vehicles. An airbag device includes a box-shaped case housing a folded airbag and an inflator for generating gas to inflate the airbag, and a cover covering an opening at the top of the case. The cover includes a lid as an opposed part opposed to the airbag and provided with a tear line (a split-expected line) to split, and an open-expected flap defined by the tear line on the cover. In the event of collision or impact of a vehicle, the airbag inflated by gas generated by the inflator pushes forward the open-expected flap covering the airbag, and the tear line splits by the inflated pressure, so that a door-flap (the flap) at the lid opens.
In order to meet a recent demand for improvement of appearance of such airbag devices, covers including lids covered with covering materials such as leather are known. In such a cover covered with a covering material, the covering material is provided on the backside thereof with a recess reduced in thickness and located at a position corresponding to a tear line, so as to facilitate deployment of an airbag without the cover blocked by the covering material (refer to JP H09-183373 at page 3, and FIG. 1 to FIG. 5).
With regard to the tear line, there may be a case where an intersecting portion that intersects substantially at right angles near the outer periphery of the cover is provided corresponding to the opening characteristic required for the cover body. In such a case, there is known a cover body provided with decorative stitching (stitching lines) for reinforcing the edge portion of the intersecting portion in the covering material so that the tear line does not go beyond the intersecting portion. In this cover body, breakage going beyond the tear line is prevented by decorative stitching, and the breaking can be smoothly progressed along the desired tear line (refer to JP 2009-120038 at page 3 and FIG. 5 to FIG. 7).
When a recess reduced in thickness and decorative stitches for improving an appearance as described above are combined to obtain a cover, a covering material may cause rupture because of a pressure applied to the covering material during stitching when the recess and perforations of the decorative stitches are aligned close to each other. Further, since the covering material may split at both the recess overlapping with the tear line and the perforations of the decorative stitches when the airbag is inflated, the covering material of the cover may tear in an irregular shape, not as originally designed.
Accordingly, there is a need for improvement in covers for airbag devices in order to not only improve yields (productivity) but also improve performance of splitting in a predetermined shape when inflating airbags.